You can maximize, minimize, and otherwise vary the spin on your serve (for deception) by varying the contact point. How do you do this?
To maximize the spin, contact the ball near the tip, which is the fastest moving part of the racket when you serve, since it’s the farthest part from the wrist, which should be snapping the racket through the ball. If you really want to maximize this, you should normally contact it a little to the side of the tip. For example, for a righty serving a forehand pendulum serve, the wrist is on the right side of the racket, so the farthest part of the racket is the left side of the tip – and so you get the most spin by contacting it there.
However, maximizing spin isn’t the only thing a serve wants to do – he also wants to vary the spin. The simplest way is to simply contact the ball near the throat, which is moving much slower than the tip. The result is very little spin without changing the serving motion. If you are serving backspin, and the receiver doesn’t see the change in the contact point, he’ll think there’s more backspin on the ball then there is, and so will likely pop the ball up or go off the end. If you do serve a no-spin like this, make sure to sell it – a big follow-through!
Another way to vary the spin by varying the contact point is to change the axis of the racket’s rotation. If you serve with only a forearm motion, then the axis of rotation is the elbow. If you snap your wrist into the shot, then the axis of rotation is the wrist. But suppose, as you contact the ball, you change the axis of rotation to around the middle of the racket? Then the tip might be going down while the throat is moving sideways or up. If you contact it with the tip, you might get backspin, but if you contact it near the throat, you get sidespin, topspin, or a combination. But the receiver will see the tip moving down – vigorously! – and so will likely read it as backspin. Result? They pop it up or go off the end. Once again you have varied the spin without changing the serving motion.
These principles follow for all serves, but vary according to the specific serving motion. Start thinking about your motion, perhaps doing it in slow motion (without the ball) so you can practice varying the spin with the same motion. Then get a box of balls and practice it!